1. Field of Invention
Exemplary aspects of the present invention relate to a light source unit and a projector.
2. Description of Related Art
In related art projectors (projection display apparatuses), halogen lamps, as an older type, or ultra-high pressure mercury lamps (UHP lamps), as a modern type, have been widely used as a light source. The UHP lamps feature high luminance and high luminous efficiencies. The light source employing the UHP lamp, which is a discharge lamp, requires a high-voltage source circuit and has a large size and a heavy weight. Hence, such a light source constitutes an obstruction to the reduction of size and weight of the projector. The UHP lamp has not yet achieved a sufficient length of service life although the service life thereof is longer than that of the halogen lamp. Furthermore, it is almost impossible to control the light source employing the UHP lamp (high-speed turn-on, turn-off, or modulation). In addition, the UHP lamp requires several minutes for activation.
An LED device is being considered as a light source. The LED has an ultra-miniature and ultra-light structure as well as a long service life. Furthermore, the LED allows for free control of turn-on, turn-off and the amount of illumination light by way of the control of a drive current. Unfortunately, however, it is difficult for the state of the art to attain a sufficient luminance from a projector employing the LED as the light source. This is because the LED has a luminous efficiency of about ½ to ⅓ of that of the UHP lamp so that a small amount of light is attained from the LED operating on an upper limit of the rated current. Technological innovations have steadily been enhancing the above efficiency so that the LED may achieve an efficiency comparable to that of the current UHP lamp in the years ahead. At least in the foreseeable future, however, the status quo for the projectors with the LED light source, which are to be brought to the commercial stage, will remain unchanged. There is a related art method where LEDs are arranged in an array in order to increase the amount of illumination light. However, this method does not provide much notable effect because a light emitting point is increased in size so that the efficiency of the illumination light of an optical system is lowered.
As the last viable approach, it may be contemplated to increase the amount of illumination light from the LED. However, the amount of illumination light is limited by the rated current for the LED, as described above. The maximum amount of illumination light from the LED is automatically decided by the ratings and the luminous efficiency thereof. Considering that the rated current for the LED primarily depends upon the amount of generated heat, a cooling technique has been proposed to address the heat generation, the technique wherein a fluid having high heat conductivity is filled in a related art LED package. See, for example, JP-A-2001-36148.